1. Field of the Invention
These types of movable cradles are used in particular on buildings which have a constant or variable circular outline, such as for example chimney stacks which are circular or frusto-conical, telecommunications towers which are rotationally paraboloid, or cooling towers which are rotationally hyperboloid, or similar buildings. The movable cradles can be used for example to carry out renovation work on the concrete or to replace the anti-corrosion covering on steel structures.
2. Description of the Prior Art
The known movable cradles have a work platform, more particularly of light metal, which can be moved up and down on cables by means of special winches. At the top edge of the building there is an upper carriage which can move round in a circle. The work platform is suspended from the upper carriage by moving guide cables. These known movable cradles also have tension cables which are braced to fix the work platform in position to prevent it from swinging about radially and tangentially in the wind. These tension cables are fixed at the bottom to consoles which can be moved on rails.
The pretensioning force necessary for a safe operation is susbtantially dependent on the structural height between the upper carriage and the lower rail. Higher pretensioning forces are necessary for example for movable cradles used on the inside walls of cooling towers. In these cases additional pressure must be applied to the work platforms is those areas which are off-set outwards relative to the upper suspension point.
For movable cradles on the outside faces such buildings, additional equipment is necessary to press the work platform against the building.
This type of work platform is known from DE-OS No. 20 14 102 has a blower which produces an underpressure zone between the suspended platform and the wall in order to hold the platform against the wall by suction. Alternatively this blower can blow against the wall to produce a compressed air cushion between the wall and the work platform so that the latter is held at a certain distance from the wall by the air cushion.
DE- G No. 85 31 513 U1 describes an auxiliary structure wherein at least one flow machine producing a thrust force is mounted on or in the work platform with its pressure side on the side of the work platform remote from the wall and directed away from the wall.